Validation of the Health Assessment Questionnaire disability index in patients with gout

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Abstract
Objective To assess the psychometric properties of the Health Assessment Questionnaire (HAQ) disability index (DI) in patients with gout. Methods This study was conducted in a multicenter cohort of patients with gout whose data were collected at baseline (time 0) and 6 months later (time 6). Reliability was assessed by test–retest reliability (intraclass correlation coefficient [ICC]) and internal consistency (Cronbach's alpha coefficient). Construct validity was assessed with convergent validity (HAQ DI correlation with Short Form 36 [SF‐36]) and discriminative validity (HAQ DI correlation with clinical features). Sensitivity to change was determined by comparing HAQ DI time 0 versus HAQ DI time 6 (percentage of change, effect size, smallest real difference [SRD], and Guyatt's responsiveness index [GRI]). Results We included 206 patients (96.6% men, mean ± SD age and disease duration 56.3 ± 12.4 years and 9.3 ± 8.5 years, respectively). Of these, 52.4% had joint pain, 22.8% swelling, 32.5% reduced joint mobility, and 36.9% tophi. The mean HAQ DI score was 0.59 ± 0.77 (95% confidence interval [95% CI] 0.49–0.70). ICC (n = 36, evaluations at baseline and 5 days later) was 0.76. Cronbach's alphas were 0.91 (95% CI 0.88–0.92, P = 0.000) for the 20 HAQ DI items and 0.93 (95% CI 0.92–0.94, P = 0.000) for the 8 HAQ DI categories. The HAQ DI correlated in predictable ways with SF‐36 subscales and clinical variables, and discriminated between subgroups with and without any joint pain, swelling, and tophi. Concerning sensitivity to change (n = 167), the difference between HAQ DI time 0 and HAQ DI time 6 was 0.31 ± 0.58 (effect size 0.62, SRD 0.59, and GRI 1.91). ΔHAQ DI correlated with Δpain (r = 0.349, P = 0.000). Conclusion The HAQ DI is a valid and reliable measure of functioning in patients with gout.